Telephone system



April 1o, 192s. '4 1,665,708

c. E. LoMAx TELEPHONE SYSTEM Original Filed Dec. 6, 1922 J5 Sheets-Sheet 2 ZarEl-LEE E Lnmax I E27-g,

April 1o, 192s. 1,665,708

C. E. LOMAX TELEPHONE SYSTEM Original Filed Dec. 6, 1922 3 Sheep5-sheeg 3 if /711 v [wird -Inuenn arenca EL Umax Patented Apr. 10, 1928.

UNITED STATES PATENT ori-ucr..

CLARENCE E. LOMAX,

AUTOMATIC ELECTRIC INC., DELAWARE.

OF CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO

OF CHICAGO,

ILLINOIS, A CORPORATION OF TELEPHONE SYSTEM.

Application led December 6, 1922, Serial No. 605,149. Renewed September 26, 1927.

The present invention relates to telephone systems in general, but more particularly to automatic telephone systems; and the main object is the production of new and improved circuit arrangements particularly adapted for use in a small isolated automatic exchange, and which enable such an exchange to be manufactured very cheaply while retaining all the features necessary for modern high-class and dependable telephone service.

Such isolated exchanges are generally privately owned by an establishment that has use for an extensive intercommunicating system, such as, for example, a manufacturing establishment or a large department store.

One feature of the invention relates to improved circuit arrangements for a link circuit comprising a numerical forward selecting switch and a non-numerical line finder switch. 1

Another feature of the invention is an improved preselecting allotter which allots the next link circuit for use when the allotted one is taken for use.

Still another feature relates to the improved line and cut-off relay combination.

A still further feature has to do with the improved common signalling equipment which furnishes the necessary tones and ringing current.

The other features which are concerned mainly with the circuit details will, together with the ones named above, be explained fully hereinafter, reference being had to the accompanying Figs. 1-8, inclusive, and which show b means of the usual circuit diagrams a su ficent amount of the apparatus used in a system embodying the features of the invention to enable the invention to be understood and its utility appreciated. I

Figure 1 of the drawings showsa calling subscribers substation and line which terminates at the exchange in the banks of line finder switches and has associated with it theline circuit is shown and the common finder allotter which allots the idle findersfor use.

Fi ure 2 shows a connector permanently associated with the finder F, Fig. 1 andl having access to the line of substation A lby drawings which comprises` LC. Also, one of the finders and, also the other lines of the private automatic exchange.

Figure 3 shows the common signalling equipment which is used to supply ringing current, busy signallin current, and also dial tone to tell the calling subscriber when to begin to dial the number.

The automatic substations A and A are similar to each other, and each has the usual talking, signalling, instrumentalities. The line circuit LC and LC', in which the lines of these substations terminate, are similar to each other, and each has the usual line and cut-off' relays which, however, have novel circuit arrangements as will be pointed out hereinafter.

Each of the finders, such as the finder F, Fig. 1, and the operating mechanisms O and O of the finder allotter FA is of the well-known rotary type of switch, of which the wipers move in a forward direction only and have no normal position.

The connector C, Fig. 2, is of the wellknown vertical and rotary type and, accordingly, its bank contacts are arranged in horizontal rows or levels according to the usual and well-known practice.

In order to facilitate the detailed description of the operation of the apparatus shown, it will be assumed that the subscriber at substation A desires to converse with the subscriber kat substation A.

When the receiver is removed at substation A, line relay 14 of the line circuit LC energizes over the line conductors 11 and 12 means of vits' upper winding, which is connected to conductor 12 through armature 15v of cut-off relay 13 and its resting contact, conductor 11- bemg grounded at this time through .the resting contact of armature 17 of cut-off relay 13 and said armature, and the common conductor 25. Upon energizing, line relay 14 disconnects ground from test contact 22 and its multiples in the banks of the finders at armatures 18 and 19; connects conductor 27 with private normal convductor 28 and cut-off relay 13 at armature 18; places ground on the signal start conductor 24 at armature 19; and at armature 20 places ground through armature 16 and its resting contact on the finder start conductor 26.,

Assuming the operating mechanism O of and switch controlling the finder allotter FA to be resting with the wipers 68 and 69 on the bank contacts 72 and 73 of the nder F, line relay 37 of the finder F energizes over the following circuit: from ground by way of the common start conductor 26, resting contact of armature 85 and said armature, spring 66 of the push button P and its resting contact, wiper 69, bank Contact 73, and line relay 37 of the finder F to battery. Upon energizing, line relay 37 closesl a circuit for switching relay 36 and stepping magnet 35 in series at armature 47, and at armature 46 connects test wiper 39 of the finder F to the junction of switching relay 36 and stepping magnet Assuming the wipers 38-40, inclusive, of the finder to be standing on the bank contacts 21-23, inclusive, of the calling line, the lat ter operation of line relay 37 does not have any effect at this timev and switching relay 36 energizcs immediately. Assuming, however, that the wipers of the finder are standing on the bank contacts oit a non-calling or a busy line, switching relay 36 is short-circuited by the ground potential found by test wiper 39, and stepping magnet is operated from this same groundpotential, and the wipers of the finder are advanced step by step by the buzzer-like action of stepping magnet 35 in search of the calling line.

When the terminals of the calling line are reached, test wiper 39 encounters an ungrounded contact, and switching relay 36, being no longer short-circuited, energizcs in series with stepping magnet 35. Stepping magnet 35, however, does not energize at this time on account of the high resistance of switching relay 36. Upon energizing, switching relay 36 connects the line conductors ofthe calling line with the corresponding conductors 48 and 53 of the connector C at armatures 41 and 45; closes a point in the circuit of 'chain relay 83 at armature 42; prepares a locking circuit for itself and grounds conductor 51 at armature 44; and at armature 43 disconnects test wiper 39 from .the junction'of its own winding andstepping magnet 35, and connects it to ground, thereby placing a busy potential on private normal conductor 28 of the calling line, and closing a circuitfor cut-off relay 13 in series with the lower winding of line relay 14. Upon energizing, cut-off relay 13 disconnects ground from start conductor 26 at armature 16, thereby openinthe circuit of line relay y 37 of the finder Line relay 37, however, being slow-acting, does not deenergize immediately. As a further result of the energization. of cut-olf relay A13, it disconnects the calling bridge at armatures 15 and 17. Line relay 14, however does not deenergizevat this time but is held energized eries with cut-off relay 13 by its own lo er winding.

As a. result of conductor 51 being explained above.

grounded upon the energ1zation of relay 36 of the finder as above explained, stepping magnet 63 energizes over the following circuit: from ground by way of the vworking contactdof-armature 47 and said armature, `Working contact of armature 44 and said armature, `conductor 51, resting contact of armature 130 and said armature, conductor 52, bank contact 72, wiper 68, resting contact of spring 65 and said spring, armature 86 and its resting contact, and stepping magnet 63 to battery. Stepping magnet 63 now advances wipers 68 and 69 from engagement with bank contacts 72 and 73, and continues to advance them by its buzzer-like action until wiper 68 comes into engagementY with an ungrounded contact which denotes that an idle linder connector link is reached. The line relay of the allotted finder isnot operated, however, until another call is made for the reason that ground is removed from the start conductor 26, prior to the new finder being allotted, by cutfo relay 13 as During the time in which the wipers 68 and 69 are being rotated in Search of an idle finder connector link, relay 61 is held energized in multiple with stepping magnet 63 by its upper winding, and maintains the start conductor open at armature 85 so as to prevent the energization of the line relays of the busy nders passed over by wipers 68 and 69 in case startconductor 26 again becomes grounded, due to another call being originated, before the next finder is allotted. l

In the, connector C, line relay 102 encrgizes over the calling line in response to the previously described operation of switching relay 36 of the finder F, the lower winding of relay 102 being grounded through the common dial tone conductor 172. Upon energizing, relay 102 closes a circuit-'for release relay 103 at armature 120.v 'Release relay 103, upon energizing, opens a point in the circuit of common signal 171 at armature 124 and prepares a circuit for vertical magnet 112; places ground 'on locking conductor 175 at armature 123; and at armature 122 grounds holding conductor 52, thereby es tablishing a holding circuit for switching relay 36 of the finder F by Way of armature 44 and its working contact before the slow acting line relay 37 has had time to deenergize.

The calling subscriber now hears the dial tone, which is placed on the common conductor 172 by the signal equipment shown in Fig. 3 in a manner to be explained hereinafter, and knows that he may now call the desired number.

In response to the calling of the first di 't in the desirednumber, line relay 102 is eenergized a corresponding number of times Ain respgnse to the interruptions of its circuit at the calling substation. Upon each of the resulting deenergizations of line relay 102, an impulse of current is sent to vertical magnet 112, the first impulse of current being transmitted overv the following circuit: from ground by way of armature 120 and its resting contact, armature 124 and its working contact, contact of off-normal spring 127 and said spring, relay 104, and vertical magnet 112 to battery. By the operation of vertical magnet 112, the wipers 148-150, inclusive, of the connector are raised opposite the level of contacts in which the desired line terminates. Relay 104 is energized in series with vertical magnet 112 and, being slow-acting, retains its armature attracted throughout the vertical movement. The energization of relay 104 servies, at armature 126, to maintain the circuit of relay 104 and vertical magnet 112 intact after the ofi-normal springs have shifted, as they do upon the first vertical step. As a further result of the encrgization of relay 104, it closes a circuit for relay 101 at armature 125. Upon energizing, relay 101 closes a locking circuit for itself at armature 115; opens the point in the circuit of the common signal 171 and prepares a circuit for release magnet 111 at armature 116; places direct ground on the lower winding of line relay 102 at armature 119 and disconn ects the dial tone conductor 172 therefrom; connects up the lower talking condenser to conductor 53 at armature 117, the lower talking condenser being normally disconnected to prevent a normal flow of dial tone through the lower talking condenser and through the lower winding of impedance 105 to battery by Way of the lower winding of ring-cut-off relay 109.

At the end of the vertical movement, series relayl104 deenergizes; opens the initial circuit of relay 101 at armature 125, leaving relay 101 energized over its locking circuit which includes armature 115; and at armature 126 opens the point in its own circuit and that of the vertical magnet 112 and extlelndsv the operating circuit to rotary magnet When the calling subscriber operates his calling device in accordance with the second digit of the desired number, the corresponding deenergizations of line relay 102 result in a corresponding number of impulses being transmitted to rotary magnet 113. The circuit over which the first of these impulses is transmitted, is as follows: from ground by way of amature 120 and its resting contact, armature 124 and its working contact, normally open contacts controlled by off-normal spring 127, amature 126 and its resting contact, armature 137 and its resting contact, armature 146 and its resting contact, and rotary magnet 113 to battery. By the operation of rotary .magnet 113, the wipers 148-150, inclusive, are rotated into engagement with the bank contacts 1511-153, incluof busy relay 108, which is likely to occur during the rotary movement while test wiper 149 is passing over grounded test contacts, from opening the circuit of relay 107 and ro tary magnet 113.

It will be assumed first that the called line is busy, in which case test conductor 152 is grounded, and when test Wiper 149 arrives on test contact 152, busy relay 108 energizes through the normally closed contacts controlled and its working contact; prepares the busy signalling circuit at armature 138; opens a point in the circuit of relay 107 and rotary magnet 113 at armature 137; and at armature 136 disconnects the locking conductor 175 from the lower winding of relay 110 and prepares a locking circuit for itself.

Under these conditions, when slow-acting relay 107 deenergizes at the end of the rotary movement, it disconnects litself and rotary magnet 113 from the operating circuit at armature 135'; completes a locking circuit for busy relay 108 at the normally closed contacts controlled by armature 134; and at the normally closed contacts controlled by armature 133, places the busy tone which is on the busy signalling conductor 174, on the lower heavy talking conductor 53 by way of the lower talkin condenser and armature 117 and its working contact. By this operation, a busy signal is -transmitted back to the calling subscriber -to inform him that he cannot, for the time being, obtain the desired connection and, when the calling subscriber replaces his receiver, the

partially established connection is releasedy in the usual manner.`

It will be assumed now that the line of substation A is idle when called, as hereinbefore described. That bein the case, busy relay 108 is not energized w en the wipers of the connector come to rest on the terminals of the called line and relay 107, upon deenergizing, completes ,a circuit for the lower winding ot switching relay 110 in series withl cut-olf relay 154 and the lower windin of line relay 155 of the line'circuit L as follows: from ground by way of locking conductor 175, armature 136 of busy relay 108 and its resting contact, lower winding of relay 110, resting contact of armature 134 and said armature, normally closed contacts controlled by armature 144, test wiper 149, test contact 152, cut-oit relay by armature 144, and armature 134 1154 and the lower winding of relay 155 to battery. Cut-off relay 154, upon energizing, clears the called line of its bridge at its upper and lower armatures. The en- 'ergization of line relay 155, however, is

merely incidental at this time and does not perform any particular function.

In the connector C, switching relay 110, upon energizing, closes a locking circuit for itself first at its lightly adjusted armature 145, and then disconnects' rotary magnet 113 at armature 146 so as to prevent any further rotation of the wipers in case the calling subscriber again turns his calling device; disconnects ground from the upper terminal of relay 106 and places directground on test wiper 149 at armature 144; disconnect-s armature 134 of relay 107 from test wiper 149 at the normally closed contacts controlled by armature 144; and at armature 143 and 147 connects up the line wipers 148 and 150, whereupon ringing current is intermittent-ly projected out over the lower talking conductor to the called substation from the common ringing conductor 173, and returns by way of the upper tall;- ing conductor to battery by way of the upper winding of ring-cut-oi relay 109.

When the called subscriber responds to the ringing of his bell by removing his y receiver, ring-cut-of relay 109 energizes over the called line from ground on common ringing conductor 173, and closes a locking circuitfor itself at its lightly adjusted armature 141, and then placesl ashunt around the Vresting contact of armature 130' and said armature" at armature 140 for a reason which will be pointed out fully hereinafter; and at armatures 139 and 142 disconnects the conductors of the called line from the source of ringing current and its own upper winding. and4 extends them to the windings of.

battery feed impedance 105 by way of armature 133 and its resting contact, and the working contact of armature 121 and said armature. The called subscriber Anow receives talkin battery through the upper; winding of lmpedance 105 and the return circuit to ground is afforded through the,

lower winding of impedance 105, armature 132 and its resting'contact, and the working contact of armature-141 and said armature to the grounded locking conductor 175. The reasons for leaving the lower winding of impedance 105 ungrounded until ring-cut-otl' relay 109 energizes. is to give the calling subscriber an audible ringing signal due to the ringinv current returning through the upper winding of ring-cut-o relay 109, and inducing a tone by transformer action in the lower winding of relay 109 which is trans-v mitted to the lower talking conductor through the lower winding of impedance 105.

The calling and called subscribers may now converse with each other as desired and when the conversation is finished, they both replace their receivers.

When the receiver is replaced at the called substation A', no particular result is accomplished inthe connector C except that current merely stops owingthrough the talking-battery-feed impedance 105.

When the receiver is replaced at substation A, line relay 102 of the connector C deenergizes and opens the circuit of slow-acting release relay 103 at armature 120, at the same time closing a circuit for slow-acting relay 107. Relay 107 energizes at this time,'but does not perform any particular function. lVhen slow-acting relay 103 lets go, it removes ground from guarding conductor 52 and holding conductor 51 at armature 122, whereupon the inder connector link is rendered selectable to the linder allotter FA again and switching relay 30 of the nder 1F deenergizes: disconnects the conductors of the line of substation A from the line conductors of the connector C at armatures 41 and 42; and removes ground from test wiper 39 at armature 43, allowing relays 13 and 14 of the line circuit LC to deenergize. As a further result of the deenergization of release relay 103, it removes ground from locking conductor 175 at armature 123, thereby opening the circuit of relays 101, 109., and 110. Relay 110 deenergizes promptly.

Relay 101 and relay 109, however, being slow-acting, retain their armatures attracted for an interval. As a still further result of the deenergization of relay 103, a circuit for release magnet 111 is closed as follows: from ground by way of armature 120 and its resting contact, armature 124 and its resting contact, armature 116 and is working contact, land release magnet 111 to battery. Upon the energizationof release magnet 111,.the shaft and wipers of the connector C are restored to normal position.

When the normal position is reached, a point in the circuit of the common. alarm signal 171 is opened'y at off-normal contacts 128.

Shortly after its circuit is opened, relay 109 deenergizes and restores itsl armatures to normal. Relay 101 deenergizes after an interval, but in case the connector is in working order mechanically and hasbeen restored to normal by release magnet 111, no particular result is accomplished. Assuming, however, that the switch shaft was not restored to normal, the otnormal contacts 128 are" link from service and when such an occasion arises, a iat piece of conducting material about the size of a five-cent piece is inserted between the springs of the jack J, thereby closing a circuit for the lower Winding of relay 106. Relay 106, upon energizing under these conditions, separates conductors 51 and 52 at armature 130, and places ground on conductor 52 so as to render the finder connector link non-selectable to the finder allotter FA, and at armature 129 places a shunt around the chain contacts 42 of the finder F so as to impose the same condition on the chain circuit as is there when the finder connector link is in actual use.

It may occur occasionally that all the finder connector links become busy, and that a subscriber attempts to originate accall at this time and is unsuccessful because no inderconnector link is available. Assuming that all the finder connectors become busy, all the contact points, such as armature 42 of switching relay 36 and its working contact, in the circuit of chain relayY 83 are closed and chain relay 83 energizes; disconnects stepping magnets 63 and 64 at armatures 86 and 87 so as to prevent useless hunting operation at this time; and at armature 89 closes a circuit for relay 62. Relay 62 thereupon energizes and connects the all trunks busy tone conductor 54 with the common conductor 25 and disconnects ground therefrom, so as to give a distinctive tone to any subscriber who happens to take od his receiver at this time. It may be stated that this tone is taken from the ringing current lead through a small condenser as may be seen in Fig. 3. This small condenser cuts down the loudness of the tone considerably, but allows a tone to pass which is very much louder than either the ordinary busy signalling tone or the dial tone ordinarily received soon after the subscriber removes his receiver. For this reason, the subscriber, upon hearing the all trunks busy tone, is able to distinguish that tone by its loudness, and is informed thereby that all the connecting links are busy. The subscriber may now replace his receiver and wait a while for a trunk to become idle, or he lmay leave his receiveroff the hook and wait until his line is found by a inder.

Assuming that all the finder connector links are busy, and that several subscribers have their receivers off waiting for dial tone and are listening to the tone placed on b relay 62 of the finder allotter FA, all the subscribers who are waiting for the dial tone note the cessation of the all trunks busy tone when a. trunk becomes idle and relay 62 deenergizes due to the deenergization of cha-in relay 83. However, all the waiting subscribers, except the one whose line is found by the finder which becomes idle, hear the all trunks busy tone again when the switching relay of the finder corresponding to switching relay' 36 of the finder F energizes and closes the chain again upon finding one of the calling lines. This process, of course, is repeated until all the waiting lines have been taken care of, and the intermittent interruption of the all trunks busy tone may be exceedingly puzzling to the subscribers who hear it several times before their respective lines are found or it may even be the source of considerable annoyance. In order to furnish a means to prevent the all trunks busy tone from being interrupted while two or more subscribers are waiting at such a time, t-he locking push-button P has been provided and may be operated, when desired, to connect the working contact of armature 84 of relay 62 to the common start conductor 26. When this is done, relay 62 becomes locked up independent of chain lrelay 83 through armature 84: and its working contact and the normally open contacts of the push-button P to start conductor 26 and, consequently, does not deenergize a ain until the lines'of all the waiting subscri ers have been found, or until all the subscribers have hung up their receivers and thereby removed ground from the start conductor, in which case relay 62 deenergizes in case chain relay 83 has fallen back.

The working contact of armature 84 is not permanently connected with start conductor 26 for the reason that it may at some time be desirable to have relay 62 fall back each time the chain circuit is opened, so that an observer who is making a call may have some fair idea as to the way in which the trailc is being handled, as is determined by the frequency at which the all trunks busy tone is interrupted.

Since, the finder allotter is common to several finders, it is extremely important to guard against any mechanical trouble that may arise in the finder allotter from time to time, especially since the finder allotter must operate each time a call is made and, for that reason, receives considerable use. In order to guard against the service from being tied up owing to afmechanical failure in the finder allotter, a second .operating mechanism, which is shown inside the dotted rectangle denoted by the reference character O, has been provided and, when it is desired to do so, the push-button P may be operated with the result that the operating mechanism shown in the dotted rectangle indicated by the reference character O is disconnected at spring 65 and the substitute operating mechanism is connected up at spring 67. Also, the start conductor 26 is shifted from wiper 69 of the first operating mechanism to wiper 70 of f the second operating ,mechanism at spring 66. It may be pointed out that relay 61 is operative when the second operating mechanism is used owing to the fact that it has a second Awinding in multiple with the second operating magnet which allows it to operate pist as thoughthe rst operating mechanism Were in use.

The operation of the common signalling uipment shown in Fig. 3 will now be described. Of this equipment, the ringing interrupter relays 201-205, inclusive, and the associated marginal relay 206 will be considered first. The ringing interrupter relays 2.014205, inclusive, are provided for the purpose of interrupting t current so as to project ringing current out on a called line intermittently, and also to distribute the ringing periods of the live ringing leads so as to lower the maximum demand for ringing current in order to allow a source of ringing current of a smaller capacity to be used than would be necessary were the ringing current supplied to all the ringing leads simultaneously.

For the purpose of the following description, it will be assumed that a call is made. This results in the signal start conductor 24 being grounded as hereinbefore described. When his occurs, the rst interrupter relay 201 energizes through the resting contact of armature 242 and said armature, and in series with the low wound marginal relay 206. Marginal relay 206, however, does not energize in series with one of the interrupter relays alone, and, consequently, remains inert for the time being. In order to time the operation of the interrupter relays properl they are made slow to deenergize by t e well-known expedient of placing a copper collar around the core, and are made slow to energize by placing the copper collar around the armature end of the core rather than the opposite end. This means of making a relay slow to pull up is, of course, well-hewn to those skilled in the art, and is taken advantage or in this case merely to slow up the cycle of operation still more. In the drawings those relays vwhich are slov:r to pull up are indicated by solid black portions at the upper ends of their cores in order to distinguish them from the ordinary slow to release relays which have the lower ends of their cores cross `hatched. When relay 201 energizes, it dis- T. As a further result of the energization of relay 201, it opens a pointin the circuit of relay 203 at armature 226, and at armature 227 closes a circuit for relay 202 by wa of the resting contact of armature 234- an said armature. When this occurs, 'the marginallyl adjusted relay 206 energizesand opens the circuit of relay 201 at armature e supply of ringing g 242. Relays 201, however, remains energized 65 for an interval, owing to the fact that it is slow-acting and maintains the circuit of relay 202 closed until the latter relay energizes. Upon energizing, relay 202 shifts the ringing lead controlled thereby to the'secondary winding of the ringing current transormerat armature 222; opens a point in the circuit of relay 204 at armature 228;'and at armature 229 prepares a circuitl for relay 203. v

YVhen relay 201 deenergizes, it connects the ringing lead which it controls back to round again at armature 221; opens the circuit of the slow-acting relayy 202 at armature 227; and at varmature 226 completes the circuit of relay 203. Relay 203, upon energizing, prepares a circuit for relay 204 at armature 231; opens a point in the circuit of relay'205 at armature 230; and a't armaturev223 shifts its ringing lead in the usual manner.

When relay 202 deenergizes, it, among other things which are apparent, completes the circuit of relay 204 at armature 228, and relay 204, upon energizing, prepares a circuit for relay 205 at armature 233; opens a point in the circuit of relay 201 at armature 232- and at armature 224 shifts its ringing lead to the secondary winding of the ringing cur rent transformer,

When Vrelay 203 deenergizes, it completes the circuit of relay 205 at armature 230, and relay 205, upon energizing, closes a point in the circuit of relay 201 at armature 235; opens a point in the circuit of relay 202 at armature 234; and at armature 225 shifts .ringing lead 173 from ground to the secondary winding ofthe ringing current transformer. i

l When'relay 204 deenergizes, it opens the circuit of relay 205 at armature 233 and completes the circuit of relay 201 at armature 232. When this occurs, relay 201 ener.

,gizes again with the results hereinbefore de scribed.

lWhen relay 205 deenergizes, relay 202 energizes again as before described.

This cycle of operation is repeated over` and over as long as conductor 24 remains grounded, and the ringing leads are connected to the secondary winding of the ringing current transformer oneby one in order.

There is, however an overlapping or a time interval during W `ch tworinging leads are connected to the secondary winding of the ringing current transformer. This, however, does not cause any trouble for the reason that the ringing current transformer T and the associated vibrator are designed to supply ringing vcurrent to two leads simultaneously. .i

uThe operation of the vibrator magnet 211 and pendulum 238 will now be taken pup.`

conversing.

As a further result of the ground potential being placed on conductor 24, a circuit is closed for the high-wound slow-to-energize relay 207. This relay, however, does not become sutciently energized for a moment to attract its armature. As a further result of the ground potential being placed on conductor 24, a circuitis closed for magnet 211 in series with the lower winding of impedance 208, and in series with both windings of the choke coil impedance 212. Upon energizing, magnet 211 attracts its armature and the pendulum 238 swings to the left and short circuits magnet 211, whereupon the magnet 211 deenergizes and the pendulum swings in the op osite direction. After one or two swings o? the pendulum 238, the cycle of operation becomes steady, and the time required for one complete swing is determined by the weight attached to the pendulum.

After a time which is suliicient to allow the pendulum to pick up speed and vibrate at its full amplitude, the slow to energize relay 207 energizes and places ground on the mid-point of the primary winding of the ringing current transformer T by way of the left-hand winding of the choke coil impedance 212. After this is done, each back- Vward swing of the pendulum results in a circuit being closed for the upper section of the primar winding of the transformer T, and each orward swing of the pendulum results in a circuit being closed for the lower section of the primary winding and, consequently, an alternating current is driven through the secondary winding of the transformer T. The choke coil 212 and the con.

denser 243 are used to smooth out the flow of battery current so as to prevent the batpleasant noises while the subscribers are Since, the lower winding of impedance 208 is in series with the winding of vibratorl magnet 211, the current in the former fluctuates owin to the intermittent short-circuiting of t e latter by the vibrating pendulum 238. This fluctuating current in the lower winding of impedance 208 causes a corresponding iluctuating electro-motive force to be applied to the ldial tone conductor 172 and through the upper winding of said impedance 208. The small condenser 209 which -is connected between the right-hand terminals of the upper and lower windings, respectively, allows some of the iiuctuationsvin the E; M. F. applied to the terminals of the lower winding to pass directly across to conductor 172 so as to strengthen the dial tone without adding more turns to thel upper winding of impedance 208 and, consequently, without increasing the resistance of impedance 208 to a point at which the operation of the line relays of the various associated connectors mi ht be affected.

s a still further result of the ground potential being placed on conductor 24, a circuit is closed for the busy interrupter relay 214 by the way of armature 243 of relay 212 and its resting contact. Upon energizing, relay 214 closes a circuit for relay 212 at armature 240, and relay 212', upon energizing, opens the circuit of relay 214 at armature 243. Aft-er an interval, relay 214 deenergizes and opens the circuit of relay 212 and relay 212', upon deenergizing, again closes the circuit of relay ,214. This cycle of operation is repeated over and over as long as conductor 24 'remains grounded. It will be noted that each time winding. Consequently, relay 213 imme diately deenergizes again and, .as a result, buzzes at a high rate of speed as long as relay 212 is energized and start conductor 24 grounded. Obviously, since relay 212 deenergizes at intervals, as pointed out above, the buzzing of relay 213 is interrupted at intervals, of which the time depends upon the adjustments of the relays 212/and 214. The operation of relay 213 causes an intermittent buzzing tone to be placed on the busy signalling conductor 174 through the condenser 244.

When ground is removed from start conductor 24, itis obvious that the ringing interrupterA relays, the vibrator, and the busy signalling relays stop operating. tery from being noisy, and causing un- 1 In a private automatic exchange, special services are commonly provided for such as, for example, a common call system, a conference call system, and others lof a somewhat similar nature. The connector C, Fig. 2, is arranged to disconnect battery and ground from the back bridge on the tenth level and to repeat impulses in order to provide for such services. In order to give an understanding of the functions of the connector C when raised to the tenth level and brought into engagement with one of the set of contacts in that level, reference may be had to the co-pendiiig application of Jones, SerialNo. 443,654, tiled February 9, 1921, which shows a private automaticvexchange connector having access on a certain setof contacts to a conference call connector. x

In order to explain the operation of the connector C when used as arepeater, it will be assumed that a subscriber has linitiated a call; is using the connector C, and has operated his calling device in accordance with the `is the digit dialled when any special service is desired. The various relay operations which take place when the Jfirst digit in a number is called, occur at this. time as described hereinbefore, and vertical magnet 112 raises the associated wipers opposite the tenth level of bank contacts, whereupon the tenth level springs are operated and contact 114 is closed, thereby closing the following circuit for ring-cut-o relay 109: from ground by way of armature 144 of switching relay 110 and its resting contact, contacts 114 of the tenth level springs, and the upper winding of ring-cut-otf relay 109 to battery. Upon energizing, ring-cut-otf relay places the circuitsin such a condition that no ringing current will be projected when the wipers are moved into engagement f with the desired set of contacts, and also places a shunt around armature 130 of relay 106 and its resting contact to prevent the ground potential from being removed from holding conductor 51 upon the energization of relay 106, which occurs subsequently.

Upon the next operation of the calling subscribers calling device, the wipers 148- 150, inclusive, are brought into engagement with the desired set of bank contacts and the usual busy test is made. Assuming the trunk terminating in these contacts to be idle, switching relay 110 energizes through test wiper 149 from battery on the test conductor of the trunk as shown in the J ones application above referred to, and connects up the line wipers and performs the other operations hereinbefore described. Vlen armature 144 breaks away from its resting contact, the shunt is removed trom the upper winding of relay 100, whereupon relay 106 energizes in series with the upper winding of ring-cut-O relay 109, and at armatures 131 and 132 disconnects battery and Ground from vthe windings of the battery ljeed impedance 105 and connects the windings together, thereby closing a holding ,bridge across the line conductors of the seized trunk, whereupon the line and release relays of the seized trunk energize in the usual manner.

ll on each ot the subsequent operationsv ture 133 disconnects t e upper iine wiper from tlie upper talkin condenser and closes the bridge across the e` wipers by a more direct path which is exclusive of the windings o' impedance 105. This is the usual expedient made use of in order to obtain a better repeating circuit.

When the calling subscriber replaces his receiver, ,the connector C is released in the usual manner, and the seized switch is released in response to the opening of the bridge across the line Wipers of the connector C at armature 121 of line relay 102.

lVhat is claimed is:

1. In a telephone system, a line, a line circuit therefor comprising a line relay connected thereto and a cut-olf relay for disconnecting said line relay from said line, line finders for finding said line vwhen a call is made thereover, connectors forconnecting with said line when it is called, said line relay energizing alone when a call is made over said line, and said line and cut-0E relay energizing in series whenever said line is found by a finder or is connected with by a connector. x

2. In a nder system, a plurality ot nders an allotter for alloting an idle one for use when the allotted one isI taken for use, said allotter comprising two operating mechanisms and a group of relays common to both said voperating mechanisms, and a manually operable device for discnnecting either operating mechanism from the associated relays and substituting the other operating mechanism.

3. In a telephone system, a plurality of lines, a plurality of finders for inding the calling ones of said lines, a relay operated when all of said nders are busy, means controlled by said relay for placing a tone on all unfound lines, and means for maintain -ing said relay in said operated position independent of the busy or idle condition of said finders when there `is an untound calling line.

4. An automatic switch having wipers, said wipers having a normal position, means for moving said wipers from their normal position to e'ect a connection, a release magnet for restoring said wipers to their normal position, a slow-acting release relay energized under the control ot' a calling line, a second slow-acting relay maintained energized by said release relay, means for opening the circuit of said slow-acting release relay when a call is terminated, circuit, connections such that said release relay, on falling back, opensthe circuit ot said second slowacting relay and closes the circuit of said release magnet, circuit connections such that said second slow-acting relay, on falling back, opens the circuit of said release mag-I net and also closes an alarm circuitin case saitll wipers have not been returned to norma f 5. In* a telephone system, a line, a nder switch, line and cut-off relays for said line,

lUU

a circuit for said line relay excluding the cut-off .relay completed when a call is initiated, a circuit for starting said finder completed responsive to the energization of said line relay, and a circuit including both relays completed by said iinder whenthe line is found. I

6. In a telephone system. a line, a finder switch, a line relay normally connected to said line, a cut-olf relay for disconnecting said line relay, circuits controlled by said line' relay for starting said finder and for rendering the said line selectable to said finder, said starting circuit being maintained closed until the said line is found,

- means for energizing said cut ci relay when the line is found and means for maintaining the line relay energized after it is disconnected from the line.

. in a finder system, an allottcr comprisving two separate switches, a finder start circuit, means in both switches for extending said circuit to idle nders, an allotter control circuit, and means for associating said control circuit with either one of said switches independent of the other. f 8. In a telephone system, a group of lines, a group of finder connector link circuits for extendingsaid lines when calling, a relay and means controlled thereby for giving a calling subscriber a busy signal in case all said link circuits are busy when the call is initiated, a circuit for said relay including serially related contacts in each finder, an contacts in each connector for shunting the series contacts inthe associated finder.

9. In a telephonesystem, a group of lines, a group of finder connector link circuits for extending said lines when calling, a relay and means controlled thereby for giving a calling subscriber a busy signal in case all said link circuits arerbusy when the call is initiated, a circuit for said relay including serially related contacts in each finder, contacts 1n each connector for shunting the series contacts in the associated inder, 'and means operated b an attendant for controlling the closure o said shunt contacts.

10. In a telephone system, a line, a link circuit including a finder and a connector for extending said line, a slow acting relay in said connector controlling the release of said Ender. a second slow acting relay in said connector, and a release magnet in said connector controlled jointly by said rela s.

1l. In a telephone system, finders or extending callino lines, means controlled over a circuit inclu ing serially related contacts in each nder for signalling a calling line in case all said finders are busy, and means manually controlled at will for shuntiug said contacts.

12. In a telephone system, iinders for extending calling lines, means controlled over a circuit including serially related pairs of controlle contacts in each finder for signalling a calling line in case all said finders are busy, and means manually controlled at will for shunting said pairs of contacts separately.

13. In a telephone system, a switching dcvice terminating a trunk line, means for seizing said trunk line and for operating said device. a firstrelay' operated when said trunk line is seized, a second relay initially operated when said switch is operated, the operation of said second relay being thereafter under the control of said irst relay, and a release circuit for said device jointly controlled by both said relays.

14. In a telephone system, link circuits for extending callin lines, a signalling device initially rendere effective responsive to all said link circuits becoming busy, and means for maintaining said device effective while any calling line is waiting to be extended.

15. In a tele hone system, link circuits for vextending callingkl lines, a signalling device,

means responsive\to all said link circuits becoming busy for initially rendering said signallin device effective, and means jointly by said first means and by calling lines waiting to be extended for maintaining said device effective.

16. In a telephone system, an automatic switch, subscribers lines terminating'in the banks of said switch, means for operating said switch to connect with a subscribers line, means including a switching relay for signalling said subscriber, a ring cut-oli relay and a third relay for placing a bridge" across the talking conductors of said switch, means responsive to a partial operation ot said switch for closing a circuit for said ring cut-olf relay in series with said third relay, said ring cut-olf relay operating thereover, and means for delaying the operation of said third relay until said switching relay is operated.

17. In a telephone system, a group ot lines, a group of finder connector link circuits for extending said lines when calling, a relay and means controlled thereby for giving a callin subscriber a busy signal in case all said link circuits are busy when a call is initiated, a circuit for said relay including serially related contacts in each finder, and means outside of each finder for shunting thc series contacts therein to mark that iinder in use. 18. In a telephone system, a plurality of subscribers lines, an automatic switch for connecting any two of said lines together, said switch havinga normal position, a release magnet in said switch for returning the switch to its normal position for disconnectin said lines, a relay, and an energizing circlnt-for said magnet controlled by said relay, said rela having means for closing a point in sai circuit and for opening it shortly after said magnet energizes for preventing said magnet from bnrning up should the switch fail to return to its normal position.

19. In a telephone system, an automatic 5 switch, a release magnet therefor; a circuit,

for said magneha relay for completing said release magnet circuit to energize said relay,

.v a second relay having means for preparing CLARENCE E. LMAX. 

